Investing a lump sum just means sticking a large chunk of money into the market all at once. This sounds like an obvious point but I am including it here only to contrast it with the next two articles on dollar cost averaging and value averaging.

There is nothing really wrong with putting your money into the market as a single lump sum. Markets do trend upward over time and hence one would expect that any delay could prove costly in terms of missed gains. On the other hand markets don't always go up over the short term of course and so sometimes it can be a good idea to wait a bit.

How do you know if you should wait or invest right now? You don't know, there is no way to predict the correct answer in advance. What you can do, if you are a bit more cautious, is to invest a bit of money now and the rest in chunks over the next couple of months, couple of years or even next couple of decades.

Two strategies for spreading out your investments are dollar cost averaging, where you invest in equal sized chunks on a regular basis, and value averaging, where you vary the amount you are putting into the market in accordance with market fluctuations.